Article

What is MRI Contrast?

Friday, February 01, 2019

As medical imaging technology advances and becomes more prevalent worldwide, patients are becoming more familiar with magnetic resonance imaging (MRI) and the value this modality provides to healthcare. Many people are aware that an MRI scanner is a large cylindrical machine that creates a powerful magnetic field around a patient. Furthermore, it is known that MRI is raising the standard for high resolution images, as they create extremely detailed images of soft tissue within the body; providing significant diagnostic and prognostic information.

However, patients may be unaware of the critical role that contrast plays in MRI. Magnetic resonance imaging is unique to other modalities such as X-ray and CT scans, because it may employ the use of gadolinium-based contrast agents to help add clarity and decipherability to the MRI image.

What is MRI contrast?

A contrast MRI occurs only when ordered and approved by a patient’s physician. This means that a gadolinium-based “dye” will be injected into the patient’s arm intravenously. This contrast medium will enhance the image quality, allowing the radiologist to be more accurate and confident in their diagnosis. Contrast materials are not dyes that permanently discolor internal organs; they are substances that temporarily change the way imaging modalities view and interact with the body.4 When the imaging exam is complete, the contrast material is either absorbed by the body or eliminated through urine.

Not all MRIs require the use of a contrast agent, in fact many MRI exams are effective for imaging the body’s organs without one. However, the decision of whether to use contrast during a scan is dependent on the type of condition present in the patient and the health history of the patient. Furthermore, when a very detailed image is necessary to evaluate a specific problem area of the body, then a contrast will typically be employed. By adding contrast to the veins of a patient, it enhances the visibility of inflammation, tumors, blood vessels, and the blood supply of certain organs.1

Three benefits of MRI contrast are:

In most cases, if contrast is used during an MRI then there will not be a need for additional scans, due to the enhanced nature of the initial MRI.

Contrast MRIs are superior at measuring and assessing tumors. The addition of contrast can make it possible to detect even the smallest of tumors and provide information regarding the exact location of the tumor.

A radiologist can interpret a contrast MRI better, because they can produce better quality images and have more clarity.

Why is contrast useful in MRI?

An MRI image is made up of shades of grey, varying from black to white. When a gadolinium dye is injected into a patient’s bloodstream, it helps “illuminate” certain tissues, making them easier to detect and assess for the radiologist. For example, when imaging the human body, air and hard bone do not give off an MRI signal, therefore these areas appear black or very dark on the scan. However, bone marrow, spinal fluid, blood, and soft tissues will vary in dark to light, depending on the amount of fat and water present in the tissues, and the specific machine settings used.

Once scanned, the radiologist can compare the size and distributions of the light and dark areas to assess normal and abnormal tissues.2 When contrast is added to a patient’s bloodstream during a scan, the targeted tissues will appear to glow bright white, making them very easy to detect and assess. This is extremely valuable when imaging tumors in the central nervous system and major body organs, such as the brain. Contrast can aid in detecting the tumors, determine whether they are benign or malignant, what stage they are at, and whether they have metastasized.3

Potential safety concerns of MRI contrast

Even though a contrast MRI provides extremely valuable information, a physician will not typically order an MRI with contrast unless deemed absolutely necessary. For example, in most cases sports injuries, work related injuries, and back pain do not typically require intravenous contrast exams.

When a contrast MRI is ordered, it is important that a physician ensures it is safe for each patient individually. In general, gadolinium-based contrast agents are considered very safe. While some concerns have been raised over the years about contrast agents, the Food and Drug Administration in the U.S has stated that there is not clinical evidence directly linking gadolinium to adverse health effects in patients. However, there is a small percentage of possibility that side effects caused by the dye may occur.

The contrast material used in MR is very unlikely to produce an allergic reaction, however it has occurred in a very small percentage of patients. These patients may experience symptoms such as itch eyes and hives. In most cases of allergic reaction, the symptoms are very mild and easily controlled by medication; severe reactions are extremely rare.

In addition, gadolinium-based contrast agents should be withheld from patients who have severe kidney disease. Kidneys that are not functioning properly may have issues processing the contrast agent and removing it from the body. This could result in a condition called nephrogenic systemic fibrosis (NSF), a very rare disease that results in the thickening of the skin, organs, and other tissues.4 However, in patients with normal kidney function, about 90% of the contrast material is removed from the body within 24 hours.1

Another potential health concern regarding contrast in an MRI pertains to contrast material retention in the body. A study in 2014 was released showing that about one percent of the injected dose of gadolinium may be retained in different organs of the body, including the brain.1 There is no clinical evidence shown that this gadolinium retention presents any adverse effects to patients, however it is a factor that physicians should consider when ordering a contrast MRI.

Last, studies have shown that contrast agents should not be used during an MRI for women who are pregnant or think that they may be pregnant. The gadolinium dye is associated with increased health risks to the fetus, however the MRI itself may be considered safe for both the pregnant woman and the fetus.

The use of contrast agents during an MRI is a factor that can make this imaging modality effective and valuable. While there are very few safety concerns regarding the contrast dye, in the case of many patients the use of a contrast agent can provide valuable diagnostic and prognostic information that it may be worthwhile. Consulting with a physician is recommended as each patient and scenario presents different circumstances and may lead to different decisions of using or not using a contrast agent.